Radio Communication Device and Radio Communication Method

ABSTRACT

When communication quality exceeds the first threshold, the radio communication terminal  300  starts connection with the radio communication system  120  and establishes the radio link L 2  to the radio communication system  120 . Further, a handover from the radio link L 1  to the radio link L 2  is performed when the communication quality exceeds the second threshold after the establishment of the radio link L 2 , the second threshold corresponding to communication quality degraded than that indicated by the first threshold.

TECHNICAL FIELD

The present invention relates to a radio communication device thatperforms radio communication by connecting to a first radiocommunication system and to a second radio communication is systemdifferent from the first communication system, and also relates to aradio communication method.

BACKGROUND ART

Recently, with the advancement in radio communication technologies, anenvironment is being developed in which a mobile radio communicationdevice, such as a mobile phone terminal, can simultaneously use multipleradio communication systems having different physical-layer schemes. Forexample, the radio communication systems include a mobile phone system,a wireless broadband system such as iBurst, and a wireless MAN systemsuch as Wi-MAX.

To improve convenience for the radio communication device using suchmultiple radio communication systems, IP mobility protocols are defined,such as Mobile IPv6 (see Non-patent Document 1) and NEMO Basic Support(see Non-patent Document 2) (for instance, Non-patent Documents 1 and2).

Non-patent Document 1: Johnson, D., Perkins, C. and Arkko, J, “MobilitySupport in IPv6 RFC3775,” IETF, 2004

Non-patent Document 2: Devarapali, V, et al., “Network Mobility (NEMO)Basic Support Protocol, RFC3963,” IETF, 2005

DISCLOSURE OF TILE INVENTION

In a handover to a different radio communication system in conformitywith the above-described conventional IP mobility protocol(specifically, in a link-layer handover), the followings are performedsequentially: (1) disconnecting connection to a radio communicationsystem (handover source) of a radio communication system to which aradio communication device is being connected; (2) connecting to ahandover-target radio communication system; and (3) performing handoverto the handover-target radio communication system.

For that reason, to avoid packet loss and the like occurring in ahandover to a different radio communication system, the radiocommunication device needs to be constantly connected to multiple radiocommunication systems. This causes a problem of an increase in powerconsumption by the radio communication device, thereby shortening theduration of a battery.

The present invention has been made in consideration of suchcircumstances, and has an objective of providing a radio communicationdevice and a radio communication method, with which a handover can beperformed with reduced power consumption and with less chance of packetloss, when multiple radio communication systems employing differentphysical-layer schemes are used.

The present invention has the following characteristics to solve theproblems described above. First of all, a first characteristic of thepresent invention is summarized in that a radio communication device(radio communication terminal 300) includes: a radio communication unit(radio communication unit a 301, 303) configured to perform radiocommunication by connecting to a first radio communication system (radiocommunication system 110) and to a second radio communication system(radio communication system 120) different from the first radiocommunication system; and a mobility manager (mobility manager 304)configured to manage mobility from the first radio communication systemto the second radio communication system, and the radio communicationdevice includes: a communication quality acquirer (communication qualityacquirer 305) configured to acquire communication quality of a firstradio link (radio link L1) established with the first radiocommunication system; a communication quality determination unit(communication quality determination unit 307) configured to determinewhether or not the communication quality acquired by the communicationquality acquirer exceeds a first threshold (threshold TH1) or a secondthreshold (threshold TH2) corresponding to the communication qualitydegraded than that indicated by the first threshold; and a handovercontroller (handover controller 309) configured to control a handoverfrom the first radio communication system to the second radiocommunication system, wherein when the communication qualitydetermination unit determines that the communication quality exceeds thefirst threshold, the handover controller starts connection with thesecond radio communication system and establishes a second radio link(radio link L2) with the second radio communication system, and when thecommunication quality determination unit determines that thecommunication quality exceeds the second threshold after the secondradio link has been established, the handover controller performs ahandover from the first radio link to the second radio link.

According to such a radio communication device, when the communicationquality of the first radio link established with the first radiocommunication system exceeds the first threshold, the radiocommunication device starts connection with the second radiocommunication system, namely, establishment of the second radio link tothe second radio communication system. Further, a handover from thefirst radio link to the second radio link is performed when thecommunication quality of the first radio link exceeds the secondthreshold after the establishment of the second radio link, the secondthreshold corresponding to communication quality degraded than thatindicated by the first threshold.

Accordingly, when the first radio link offers good communicationquality, the radio communication device does not connect to the secondradio communication system. This makes it possible to reduce powerconsumption by the radio communication device, namely, to extend theduration of the battery.

Moreover, since the second radio link is already established when ahandover is performed in response to the fact that the communicationquality of the first radio link exceeds the second threshold, drasticcommunication-quality deterioration, such as packet loss in a handover,can be avoided. Further, since the second radio link is alreadyestablished when a handover is performed, a prompt handover can beaccomplished.

A second characteristic of the present invention is according to thefirst characteristic of the present invention, and is summarized in thatthe handover controller causes the radio communication unit to transmitthe same packets (IP packet P) simultaneously via the first radio linkand the second radio link, and when the radio communication unit hasreceived a packet via the second radio link, the handover controllerdisconnects the first radio link.

A third characteristic, of the present invention is according to any oneof the first and the second characteristic of the present invention, andis summarized in that the handover controller includes a mediaindependent handover function (MIH function 311) not depending on aconfiguration of a physical layer of each of the first radiocommunication system and the second radio communication system, and themedia independent handover function performs the handover based on aninstruction from a protocol (MIH user 313) positioned in a layer higherthan the media independent handover function.

A fourth characteristic of the present invention is summarized as aradio communication method of performing radio communication byconnecting to a first radio communication system and to a second radiocommunication system different from the first radio communicationsystem. The radio communication method includes the steps of: acquiringcommunication quality of a first radio link established with the firstradio communication system; determining whether or not the communicationquality acquired exceeds a first threshold; and when it is determinedthat the communication quality exceeds the first threshold, startingconnection with the second radio communication system and establishing asecond radio link with the second radio communication system;determining whether or not the communication quality exceeds a secondthreshold corresponding to the communication quality degraded than thatindicated by the first threshold; and when it is determined that thecommunication quality exceeds the second threshold after the secondradio link has been established, performing a handover from the firstradio link to the second radio link.

According to the characteristics of the present invention, a radiocommunication device and a radio communication method can be provided,with which a handover can be performed with reduced power consumptionand with less chance of packet loss, when multiple radio communicationsystems employing different physical-layer schemes are used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an overall schematic configuration of acommunication network including a radio communication device accordingto an embodiment of the present invention.

FIG. 2 is a diagram showing a functional block configuration of theradio communication device according to the embodiment of the presentinvention.

FIG. 3 is a diagram showing a protocol stack implemented by the radiocommunication device according to the embodiment of the presentinvention.

FIG. 4 is a diagram showing an internal sequence followed when the radiocommunication device according to the embodiment of the presentinvention performs a handover.

FIG. 5 is a diagram showing time transition of the communication qualityof radio signals transmitted from a radio communication system accordingto the embodiment of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

Next, embodiments of the present invention will be described.Specifically, what will be described are: (1) an overall schematicconfiguration of a communication network, (2) a functional blockconfiguration of a radio communication device, (3) an operation of theradio communication device, (4) functions and effects, and (5) otherembodiments.

Note that, throughout the following descriptions of the drawings, thesame or like parts bear the same or like reference numerals. It shouldbe noted, however, that the drawings are schematic, and that thedimensional proportions and the like are different from their actualvalues.

Accordingly, specific dimensions and the like should be inferred basedon the description given below. Moreover, dimensional relationships anddimensional proportions may differ from one drawing to another in someparts, of course.

(1) Overall Schematic Configuration of Communication Network

FIG. 1 is a diagram showing an overall schematic configuration of acommunication network 10 including a radio communication terminal 300that constitutes a radio communication device in the present embodiment.As FIG. 1 shows, the communication network 10 includes an Internet 100,a radio communication system 110, and a radio communication system 120.

In the embodiment, the radio communication system 110 is configured by awireless MAN system. Specifically, the radio communication system 110 isa radio communication system in conformity with iBurst. The radiocommunication system 110 includes a radio base station 111 performingradio communication with the radio communication terminal 300.

In the embodiment, the radio communication system 120 is configured by amobile phone system.

Specifically, the radio communication system 120 is a third generationmobile phone system employing a CDMA scheme. More specifically, theradio communication system 120 is a radio communication system inconformity with a scheme (such as cdma2000 1x-EVDO) capable ofhigh-speed IP packet communications. The radio communication system 120includes a radio base station 121 performing radio communication withthe radio communication terminal 300.

A home agent 210 and an IP phone terminal 220 are connected to theInternet 100.

The home agent 210 is a home agent in conformity with Mobile as IPv6.The home agent 210 acquires a care-of address (CoA) from the radiocommunication terminal 300. The home agent 210 associates the care-ofaddress acquired from the radio communication terminal 300, with a homeaddress (HoA) being a fixed IP address identifying the mobilecommunication terminal 300.

The IP phone terminal 220 is a phone terminal using Voice over IP(VoIP). The IP phone terminal 220 transmits and receives VoIP packetsvia the Internet 100.

The radio communication terminal 300 is capable of radio communicationby connecting to the radio communication system 110 and the radiocommunication system 120. Specifically, the radio communication terminal300 establishes a radio link L1 with the radio base station 111 andperforms radio communication via the radio link L1. Likewise, the radiocommunication terminal 300 establishes a radio link L2 with the radiobase station 121 and performs radio communication via the radio link L2.

To perform radio communication by connecting to the radio communicationsystem 110 and the radio communication system 120 which are different inat least physical-layer schemes they employ, the radio communicationterminal 300 has two different radio communication units, specifically,radio communication units 301 and 303 (not shown in FIG. 1, see FIG. 2).

In the embodiment, the radio communication terminal 300 transmits andreceives VoIP packets to and from the IP phone terminal 220 by using oneof the radio communication system 110 and the radio communication system120 or using both of the radio communication systems at the same time.In the embodiment, the radio communication terminal 300 uses the radiocommunication system 110 (iBurst) preferentially over the radiocommunication system 120 (cdma2000 1x-EVDO). The radio communicationterminal 300 uses the radio communication system 120 when unable toobtain desired communication quality from the radio communication system110 and therefore unable to use the radio communication system 110.

Moreover, to extend the duration of a battery 320, the radiocommunication terminal 300 does not connect to both the radiocommunication systems for a long time (so-called constant connection).

(2) Functional Block Configuration of Radio Communication Device

Next, a description will be given of a functional block configuration ofthe radio communication terminal 300 constituting the radiocommunication device in the embodiment. Specifically, of the radiocommunication terminal 300, an overall block configuration and aprotocol stack of a handover controller will be described.

(2.1) Overall Block Configuration

FIG. 2 is a diagram showing a functional block configuration of theradio communication terminal 300. As FIG. 2 shows, the radiocommunication terminal 300 includes a radio communication unit 301, aradio communication unit 303, a mobility manager 304, a communicationquality acquirer 305, a communication quality determination unit 307, ahandover controller 309, and a battery 320. It should be noted that onlythe functional blocks relating to the present invention are describedhere, and that the radio communication terminal 300 includes otherfunctional blocks (e.g., a baseband processor and a user interface unit)that are not shown.

The radio communication unit 301 performs radio communication inconformity with iBurst employed in the radio communication system 110.

The radio communication unit 303 performs radio communication inconformity with cdma2000 1x-EVDO employed in the radio communicationsystem 120.

The mobility manager 304 manages mobility of the radio communicationterminal 300 from the radio communication system 110 to the radiocommunication system 120, and from the radio communication system 120 tothe radio communication system 110.

Specifically, the mobility manager 304 performs processing necessary forobtaining IP mobility of the radio communication terminal 300. In theembodiment, according to NEMO Basic Support, the mobility manager 304performs the processing necessary for obtaining IP mobility of the radiocommunication terminal 300.

As mentioned above, in the embodiment, the radio communication terminal300 uses the radio communication system 110 (iBurst) preferentially overthe radio communication system 120 (cdma2000 1x-EVDO). In other words,when the radio link L1 offers good communication, quality, the radiolink L2 is not established, so that the radio communication terminal 300does so not connect to the radio communication system 120 (radio basestation 121). Accordingly, to extend the duration of the battery 320,when the radio link L1 offers good communication quality, no power issupplied to the radio communication unit 303 performing radiocommunication in conformity with cdma2000 1x-EVDO employed in radiocommunication system 120.

The communication quality acquirer 305 acquires the communicationquality of the radio link L1 established with the radio communicationsystem 110. In addition, the communication quality acquirer 305 acquiresthe communication quality of the radio link L2 established with theradio communication system 120.

Specifically, the communication quality acquirer 305 acquires thefollowing communication quality parameters regarding the radio link L1:

(a) signal-to-interference-plus-noise ratio (SINR)

(b) receive signal strength indication (RSSI)

(c) transmission power

(d) uplink and downlink throughputs

Further, the communication quality acquirer 305 acquires the followingcommunication quality parameters regarding the radio link L2:

(a) SINR

(b) RSSI

(c) DRC (Data Rate Control)

The communication quality determination unit 307 determines whether thecommunication quality acquired by the so communication quality acquirer305 exceeds a predetermined threshold or not. Specifically, as FIG. 5shows, the communication quality determination unit 307 determineswhether the communication quality (specifically, RSSI) acquired by thecommunication quality acquirer 305 exceeds a threshold TH1 (firstthreshold) or not. In addition, the communication quality determinationunit 307 determines whether or not the communication quality exceeds athreshold TH2 (second threshold) corresponding to communication qualitydegraded than that indicated by the threshold TH1.

In the embodiment, regarding the radio link L1, the communicationquality determination unit 307 can set the threshold TH1 and thethreshold TH2 for the following communication quality parameters:

(a) RSSI

(b) SINR

(c) rate of transmitting data

(d) rate of receiving data

Further, regarding the radio link L2, the communication qualitydetermination unit 307 can set the threshold TH1 and the threshold TH2for the following communication quality parameters:

(a) RSSI

(b) carrier-to-interference ratio (CIR)

(c) transmission power

The handover controller 309 controls a handover from the radiocommunication system 110 to the radio communication system 120.

Specifically, the handover controller 309 starts connection with theradio communication system 120 when the communication qualitydetermination unit 307 determines that the communication quality of theradio link L1 exceeds the threshold TH1. Moreover, the handovercontroller 309 establishes the radio link L2 with the radiocommunication system 120.

Further, the handover controller 309 performs a handover from the radiolink L1 to the radio link L2 when the communication qualitydetermination unit 307 determines that the communication quality of theradio link L1 exceeds the threshold TH2 after the establishment of theradio link L2.

The handover controller 309 is capable of causing the radiocommunication unit 301 and the radio communication unit 303 tosimultaneously transmit the same packets, or specifically, IP packets P,via the radio link L1 and the radio link L2, respectively. In addition,the handover controller 309 can disconnect the radio link L1 when theradio communication unit 303 receives the IP packet P via the radio linkL2.

The battery 302 supplies power necessary for operations of each of thefunctional blocks constituting the radio communication terminal 300.

(2.2) Protocol Stack of the Handover Controller

FIG. 3 shows a protocol stack 310 implemented by the mobility manager304, the communication quality acquirer 305, the communication qualitydetermination unit 307, and the handover controller 309. As FIG. 3shows, the protocol stack 310 includes a link layer 301 a, a link layer303 a, a MIH (Media Independent Handover) function 311, and a MIH user313.

The link layer 301 a provides a function for an interface (devicedriver) with the radio communication unit 301. Likewise, the link layer303 a provides a function for an interface (device driver) with theradio communication unit 303.

The MIH function 311 is a media independent handover function notdepending on the configuration of a physical layer of each of the radiocommunication system 110 and the radio communication system 120. In theembodiment, the MIH function 311 is configured by a media independenthandover function defined in IEEE802.21. In the embodiment, the MIHfunction 311 supports the function of the handover controller 309.

The MIH function 311 perform a handover from the radio link L1 to theradio link L2, according to an instruction by the MIH user 313 being aprotocol positioned in a layer higher than the MIH function 311.

The MIH function 311 receives LINK events from the link layers 301 a and303 a, and transmits LINK commands including a request for acquiringcommunication quality, a handover command, and the like.

The MIH user 313 is positioned in a layer higher than the MIH function311. The MIH user 313 communicates with the MIH function 311. In theembodiment, the MIH user 313 is configured by NEMO Basic Support or thelike. Further, the MIH user 313 includes Multiple Care-of AddressRegistration (MCoA) being an expanded specification of Mobile IPv6/NEMOBasic Support.

The MIR user 313 further supports the functions of the communicationquality acquirer 305 and the communication quality determination unit307.

Specifically, the MIR user 313 receives MIH events from the MIH function311 and transmits MIH commands by including means for requestingacquisition of communication quality and means for instructing ahandover.

(3) Operation of Radio Communication Device

Referring to FIGS. 4 and 5, a description will next be given of anoperation of the radio communication terminal 300 constituting the radiocommunication device in the embodiment. Specifically, a description willbe given of an operation of the radio communication terminal 300performing a handover from the radio communication system 110 to theradio communication system 120.

FIG. 4 is a diagram showing an internal sequence followed when the radiocommunication terminal 300 performs a handover from the radiocommunication system 110 to the radio communication system 120. Here,assume that the radio communication terminal 300 has established theradio link L1 with the radio communication system 110 (radio basestation 111), and has been transmitting and receiving VoIP packets toand from the IP phone terminal 220.

FIG. 5 is a diagram showing time transition of the communication qualityof radio signals transmitted from the radio communication system 110(wireless MAN system) and the radio communication system 120 (mobilephone system).

As FIG. 4 shows, in Step S101, the MIH user 313 requests the MIHfunction 311 to acquire the communication quality of the radio link L1.Specifically, to the MIH function 311, the MIH user 313 transmitsMIH_Get_Status.request being an MIH command requesting acquisition ofcommunication quality.

In Step S103, the MIH function 311 requests the link layer 301 a toacquire the communication quality of the radio link L1. Specifically, tothe link layer 301 a, the MIH function 311 transmitsLink_Get_Parameters.request being a LINK command requesting acquisitionof communication quality.

In Step S103A, based on the Link_Get_Parameters.request received fromthe MIH function 311, the link layer 301 a transmits an acquisitionrequest for communication quality, to the radio communication unit 301.Here, assume that RSSI is acquired as the communication quality of theradio link L1.

In Step S109, based on the acquisition request for communication qualityreceived from the link layer 301 a, the radio Communication unit 301transmits the RSSI of radio signals constituting the radio link L1, tothe link layer 301 a.

In Step S111, to the MIH function 311, the link layer 301 a transmitsthe RSSI received from the radio communication unit 301. Specifically,to the MIH function 311, the link layer 301 a transmitsLink_Get_Parameters.confirm being a LINK event including the RSSIreceived from the radio communication unit 301.

In Step S113, to the MIH user 313, the MIH function 311 transmits theRSSI received from the link layer 301 a. Specifically, to the MIH user313, the MIH function 311 transmits MIH_Get_Status.confirm being an MIHevent including the RSSI received from the link layer 301 a.

In the embodiment, the processing performed in Steps S101 to S113described above is repeated at every 500 ms. Moreover, fluctuation ofthe RSSI owing to fading of the radio signals constituting the radiolink L1 may lead to erroneous determination that the RSSI exceeds thethreshold TH1. To avoid such erroneous determination, the link layer 301a equates the numeric values of the communication quality (e.g., RSSI)acquired from the radio communication unit 301 at every 500 ms andtransmits the equated numeric value of the communication quality to theMIH function 311. Note that the link layer 303 a too can operate likethe link layer 301 a.

In Step S200, the MIX user 313 determines that the communication qualityof the radio link L1 exceeds the threshold TH1 (communication qualitydeterioration threshold). Specifically, based on the RSSI included inthe MIH_Get_Status.confirm received from the MIH function 311, the MIHUser 313 determines that the communication quality of the radio link L1exceeds the threshold TH1. It should be noted that, in the embodiment,what is meant by “exceeding the threshold TH1” so is that the RSSI fallsbelow a predetermined value (the same is true in the following).

Specifically, as FIG. 5 shows, it is determined at timing t₁ that thecommunication quality of the radio communication system 110 (wirelessVIM system), namely, the RSSI of the radio link L1 exceeds (namely,falls below) the threshold TH1.

In Step S210, the MIH user 313 requests the MIH function 311 to preparefor a handover. Specifically, to the MIH function 311, the MIR user 313transmits MIH_Handover_Prepare.request being an MIH command requestinghandover preparation.

In Step S220, based on the MIH_Handover_Prepare.request received fromthe MIH user 313, the MIH function 311 requests the link layer 303 a toestablish the radio link L2. Specifically, to the link layer 303 a, theMIH function 311 transmits Link_UP.request being a LINK commandrequesting establishment of a radio link.

In Step S230, based on the Link_UP.request received from the MIHfunction 311, the link layer 303 a starts establishment of the radiolink L2. Specifically, the link layer 303 a causes the battery 320 tosupply power to the radio communication unit 303, which has not beensupplied with power, and thus activates the radio communication unit303. The radio communication unit 303 thus activated by the link layer303 a starts connection (PPP connection setup) with the radiocommunication system 120 via the radio base station 121.

After the radio link L2 is established by the processing performed inStep 230, the radio communication terminal 300 is now connected to bothradio communication systems: the radio communication system 110 and theradio communication system 120.

In Step S240, the link layer 303 a transmits the fact that the radiolink L2 has been established, to the MIH function 311. Specifically, tothe MIH function 311, the link layer 303 a transmits Link_UP.indicationbeing a LINK event indicating that the radio link has been established.

As FIG. 5 shows, the establishment of the radio link L2 is completed attiming t₂, and the radio communication unit 303 receives radio signalsfrom the radio communication system 120 (radio base station 121).

In Step S250, based on the Link_UP.indication received from the linklayer 303 a, the MIH function 311 notifies the MIH user 313 that thehandover preparation is completed. Specifically, to the MIH user 313,the MIH function 311 transmits MIH_Handover_Prepare.confirm being an MIHevent indicating completion of handover preparation.

Note that the MIR user 313 having received theMIH_Handover_Prepare.confirm acquires a CoA assigned to the radiocommunication terminal 300 in a handover target, namely, the radiocommunication system 120.

In Step S300, as link status acquisition processing, processing similarto that performed in Steps S101 to S113 (part boxed in dotted lines inthe drawing) is repeated at every 500 ms. Moreover, in Step S300, thecommunication quality of the radio link L2 is acquired by processingsimilar to that performed in Steps S101 to S113. More precisely, uponrequest from the MIH function 311, the link layer 303 a transmits anacquisition request for communication quality, to the radiocommunication unit 303. Here, assume that RSSI is acquired as thecommunication quality of the radio link L2.

In Step S310, the MIH user 313 determines that the communication qualityof the radio link L1 exceeds the threshold TH2 (handover threshold).Specifically, based on the RSSI included in the MIH_Get_Status.confirmreceived from the MIH function 311, the MIH user 313 determines that thecommunication quality of the radio link L1 exceeds the threshold TH2.

In Step S320, the MIH user 313 requests the MIH function 311 to performa handover from the radio link L1 to the radio link L2. Specifically, tothe MIH function 311, the MIH user 313 transmits MIH_Switch being an MIHcommand requesting a handover.

In Step S330, the MIH function 311 performs a handover from the radiolink L1 to the radio link L2. Specifically, the MIH function 311switches the transmission of the IP packets P (e.g., VoIP packets) viathe radio link L1 to the transmission of the IP packets P via the radiolink L2.

As FIG. 5 shows, disconnection of the radio link L1 is completed attiming t₃, and the radio communication unit 301 stops receiving radiosignals transmitted from the radio communication system 110 (radio basestation 111).

Note that the MIH function 311 may transmit the same IP packets P viathe radio link L1 and the radio link L2 until receiving the IP packets Pvia the radio link L2.

In Step S340, to the MIH user 313, the MIH function 311 requests the MIHuser 313 to commit the handover. Specifically, to the MIH user 313, theMIH function 311 transmits MIH_Commit.request being an MIH eventrequesting a commit of the handover.

In Step S350, based on receipt of the MIH_Commit.request from the MIHfunction 311, the MIH user 313 transmits the fact that the handover fromthe radio link L1 to the radio link L2 has been committed, to the MIHfunction 311. Specifically, to the MIH function 311, the MIH user 313transmits IH_Handover Complete.request being an MIH command signifyingthat the handover has been committed.

In Step S360, based on receipt of the MIH_HandoverComplete.request fromthe MIH user 313, the MIH function 311 requests the link layer 301 a todisconnect the radio link L1. Specifically, to the link layer 301 a, theMIH function 311 transmits Link_Teardown.request being a LINK commandrequesting radio link disconnection.

In Step S370, based on the Link_Teardown.request received from the MIHfunction 311, the link layer 301 a disconnects the radio link L1.Specifically, the radio communication unit 301 having received aninstruction from the link layer 301 a to disconnect the radio linkdisconnects the connection (PPP connection) to the radio connectionsystem 110. In addition, after the connection is disconnected, powersupply to the radio communication unit 301 is stopped.

In Step S380, to the MIH function 311, the link layer 301 a transmitsthe fact that the radio link L1 has been disconnected. Specifically, tothe MIH function 311, the link layer 301 a transmitsLink_Teardown.response being a LINK event indicating the radio linkdisconnection.

In Step S390, based on the Link_Teardown.response received from the linklayer 301 a, the MIH function 311 notifies the MIH user 313 that theradio link has been disconnected. Specifically, to the MIH user 313, theMIH function 311 transmits MIH_HandoverComplete.response being an MIHevent indicating the radio link disconnection.

(4) Functions and Effects

According to the radio communication terminal 300, when thecommunication quality of the radio link L1 established with the radiocommunication system 110 exceeds the threshold TH1, the radiocommunication terminal 300 starts connection with the radiocommunication system 120, namely, establishment of the radio link L2 tothe radio communication system 120. Further, a handover from the radiolink L1 to the radio link L2 is performed when the communication qualityof the radio link L1 exceeds the threshold TH2 after the establishmentof the radio link L2, the threshold TH2 corresponding to communicationquality degraded than that indicated by the threshold TH1.

Accordingly, when the radio link L1 offers good communication quality,the radio communication terminal 300 does not connect to the radiocommunication system 120. More specifically, the radio communicationunit 303 is supplied with no power, making it possible to reduce powerconsumption of the radio communication terminal 300, namely, to extendthe duration of the battery 320.

Moreover, the radio link L2 is already established when a handover isperformed based on the fact that the communication quality of the radiolink L1 exceeds the threshold TH2. Accordingly, drasticcommunication-quality deterioration, such as packet loss in a handover,can be avoided. Further, since the radio link L2 is already establishedwhen a handover is performed, a prompt handover can be accomplished.

In the embodiment, a handover controller 309 is capable ofsimultaneously transmitting the same packets P from the radiocommunication unit 301 and the radio communication unit 303 via theradio link L1 and the radio link L2, respectively. In addition, thehandover controller 309 can disconnect the radio link L1 when the radiocommunication unit 303 receives the IP packet P via the radio link L2.For this reason, packet loss in a handover can be avoided even morereliably.

(5) Other Embodiments

As described above, the content of the present invention has beendisclosed using the embodiment of the present invention. However, itshould be understood that the present invention is not limited by thedescriptions and drawings constituting part of the disclosure. In lightof the present disclosure, various alternative embodiments will beapparent to those skilled in the art.

For example, what is described in the above-described embodiment is acase of a handover from the radio communication system 110 (radio linkL1) to the radio communication system 120 (radio link L2). However, ahandover from the radio communication system 120 to the radiocommunication system 110 may be performed in the same way.

The above-described embodiment employs the radio communication system110 in conformity with iBurst and the radio communication system 120 inconformity with cdma2000 1x-EVDO. However, the schemes employed by theradio communication system 110 and the radio communication system 120are not limited to iBurst and cdma2000 1x-EVDO. For example, the radiocommunication system 110 may be a radio communication system inconformity with mobile WiMAX. Moreover, when Mobile IP is employed,processing of registering an acquired CoA may be performed after theradio link is established in Step S230 described above.

Furthermore, more number of radio communication systems may be includedin the communication network 10.

In the above-described embodiment, the radio communication unit beingnot used is supplied with no power. Alternatively, the radiocommunication unit may be put in a state supplied with power,specifically, in a sleep state (dormant state).

As described, the present invention naturally includes variousembodiments anti the like that are not described herein. Therefore, thetechnical scope of the present invention should be defined only bymatters to define the invention according to the scope of claimsreasonably understood from the above description.

Note that the entire content of Japanese Patent Application No.2007-069564 (filed on Mar. 16, 2007) is incorporated herein byreference.

INDUSTRIAL APPLICABILITY

As described above, with the radio communication device and the radiocommunication method according to the present invention, a handover canbe performed with reduced power consumption and with less chance ofpacket loss, when multiple radio communication systems employingdifferent physical-layer schemes are used. Accordingly, the radiocommunication device and the radio communication method according to thepresent invention are useful in radio communications such as mobilecommunications.

1. A radio communication device including: a radio communication unitconfigured to perform radio communication by connecting to a first radiocommunication system and to a second radio communication systemdifferent from the first radio communication system; and a mobilitymanager configured to manage mobility from the first radio communicationsystem to the second radio communication system, the radio communicationdevice comprising: a communication quality acquirer configured toacquire communication quality of a first radio link established with thefirst radio communication system; a communication quality determinationunit configured to determine whether or not the communication qualityacquired by the communication quality acquirer exceeds a first thresholdor a second threshold corresponding to the communication qualitydegraded than that indicated by the first threshold; and a handovercontroller configured to control a handover from the first radiocommunication system to the second radio communication system, whereinwhen the communication quality determination unit determines that thecommunication quality exceeds the first threshold, the handovercontroller starts connection with the second radio communication systemand establishes a second radio link with the second radio communicationsystem, and when the communication quality determination unit determinesthat the communication quality exceeds the second threshold after thesecond radio link has been established, the handover controller performsa handover from the first radio link to the second radio link.
 2. Theradio communication device according to claim 1, wherein the handovercontroller causes the radio communication unit to transmit the samepackets simultaneously via the first radio link and the second radiolink, and when the radio communication unit has received a packet via tothe second radio link, the handover controller disconnects the firstradio link.
 3. The radio communication device according to any one ofclaims 1 and 2, wherein the handover controller includes a mediaindependent handover function not depending on a configuration of aphysical layer of each of the first radio communication system and thesecond radio communication system, and the media independent handoverfunction performs the handover based on an instruction from a protocolpositioned in a layer higher than the media independent handoverfunction.
 4. A radio communication method of performing radiocommunication by connecting to a first radio communication system and toa second radio communication system different from the first radiocommunication system, the radio communication method comprising thesteps of: acquiring communication quality of a first radio linkestablished with the first radio communication system; determiningwhether or not the communication quality acquired exceeds a firstthreshold; and when it is determined that the communication qualityexceeds the first threshold, starting connection with the second radiocommunication system and establishing a second radio link with thesecond radio communication system; determining whether or not thecommunication quality exceeds a second threshold corresponding to thecommunication quality degraded than that indicated by the firstthreshold; and when it is determined that the communication qualityexceeds the second threshold after the second radio link has beenestablished, performing a handover from the first radio link to thesecond radio link.